The present invention relates to a sliding bearing, e.g. a dynamic pressure bearing. More particularly, the present invention relates to a dynamic pressure bearing in which a shaft member is held in its sleeveportion for relative rotation to radial bearing portion.
FIGS. 1 and 2 show a general sliding bearing, e.g., a dynamic pressure bearing. There are, respectively, shown different types of dynamic pressure bearings.
Referring to FIG. 1, the first type of dynamic pressure bearing is shown, as an example. Such the dynamic pressure bearing is provided with a shaft member 1 having a shaft body portion 2a and a flange 2b on one of the end faces of the shaft body portion 2a. The flange 2b has first dynamic pressure grooves 3, 4 respectively formed on its front and back surface to act as a radial bearing portion, while the shaft body portion 2a has the second dynamic pressure grooves 5, 6, respectively, formed on its outer circumferential surface to act as an axial bearing portion.
The shaft member 1 is fitted into a sleeve portion 7, and thus the second dynamic pressure grooves 5,6 may be formed on the inner circumferential surface of the sleeve portion 7. In the dynamic pressure bearing, the fitting of the shaft member 1 into the sleeve portion 7 forms a gap between the external surface of shaft member 1 and the inner circumferential surface of the sleeve portion 7, wherein the gap acts as a flow path to allow flow of lubricating fluid.
The sleeve portion 7 has a stepped hole 8, which is formed by construction of a small diameter hole portion 8a extending toward the interior, a large diameter hole portion 8b extending toward the exterior from the small diameter hole portion 7a through a shoulder portion 8c, and a cap-fitting hole 8d extending to the exterior from the large diameter hole 8c through a first shoulder portion 8e. The shaft member 1 is fitted into the stepped hole 8 until placement of the flange 2b in the large diameter hole portion 8b. After fitting of the shaft member 1 into the stepped hole 8, a cap 9 is fitted in the cap-fitting hole portion 8d and placed on the second shoulder portion 8e for the purpose of closure of the stepped hole 8.
For fitting of the cap 9, a press fitting or adhesive bonding process is performed. The press-fitting fixation process is a simple way of handling and provides a relatively steadily fixed cap, but has problems of which it limits bearing dimensions. Herefrom, the fixation by adhesive bonding process is generally performed, because of no limitation to bearing dimensions.
Referring to FIG. 2, a second type of dynamic pressure bearing is shown. The dynamic pressure bearing is distinguished from the foregoing first type of dynamic pressure bearing body, in construction of the shaft member, protrusion of the shaft body 2a beyond the flange 2b or formation of the flange around the outer circumferential surface of the shaft member 1. In the second type of dynamic pressure bearing, the cover member 9 has an axial center hole 91 into which the shaft member 1 passes. Since other elements are of similar construction to the first type of dynamic pressure bearing as shown in FIG. 1, the descriptions are omitted.
Referring to FIG. 7, a conventional fixation of the cap 9 into the cap-fitting hole portion 8d of the sleeve portion 7 by the adhesive bonding process is shown. According to the figure, the sleeve portion 7 has a peripheral tapered edge 7a at its top, while the cover member has a perimetrical tapered edge 9a at its top. After fitting of the cap 8 into the cap-fitting hole portion 8d, an adhesive glue B is supplied into an area A where is at the peripheral and perimetrical tapered edges 7a and 9a, from above of the cap 9, and thereby penetrates into a gap G between the sleeve portion 7 and the cap 9.
Because of the guiding of the cap 9 fitted into the cap-fitting hole portion 8d, or the prevention of back-lush or play between the tubular member 7 and the cap 9 incorporated thereinto, a gap formed between the inner circumferential surface of the sleeve portion 7 and the outer circumferential surface of the cap 9 is designed for smaller dimensions. This does not accomplish complete penetration of the adhesive glue B which is infused in the area A, into the gap through slopes of the tapered edges of the sleeve portion 7 and the cap 9, and hence causes problems of which the adhesive glue B remains in the area A or on the external surfaces of the sleeve portion 7 and the cap 9, whereby provides reduced fixation of the cap into the sleeve portion 7 by and required works for removal of the adhesive glue B being left.
The present invention is devised to solve the foregoing Problems. Therefore, an object of the present invention is to allow the smooth penetration of the adhesive glue into the gap between the inner circumferential surface of the sleeve portion and the outer circumferential surface of the cap through slopes of the tapered edges.
To attain the object of the invention, an improved sliding bearing (dynamic pressure bearing) has a gap, which is formed in construction of an upper large gap portion which provides the smooth penetration of the adhesive glue thereinto, and a lower small gap portion which provides the prevention of back-lush or play between the sleeve portion and the cap thereof.
The gap with the upper wide gap and the lower narrow gap is defined by the sleeve portion provided with a second internal shoulder at its lower portion near the second shoulder, or a cap provided with a circumferential shoulder at its lower portion near the bottom.
In another embodiment, the inner circumferential surface of the sleeve portion, and the outer circumferential surface of the cap are each provided with a lateral groove in which the adhesive glue anchors thereinto. The lateral grooves have an internal top surface, which is tapered so as to allow the adhesive glue to smoothly penetrate thereinto for more effective fixation of the cap in the sleeve portion.